Such a gas-liquid contacting tray is known from GB-A-1422131. This publication describes a gas-liquid contact tray comprising a bubble area and a plurality of rectangular downcomers. The downcomer openings are so spaced in the bubble area that one downcomer opening is surrounded with bubble area at two or more of its four sides. This results in that, when the tray is used, liquid present in the space above the bubble area will enter the downcomer opening from opposite sides of the downcomer. When such trays are used in a gas-liquid contacting column two consecutive trays are so arranged that the lower end of a downcomer of the upper tray is oriented above bubble area of the tray below.
U.S. Pat. No. 5,382,390 also describes a gas-liquid contacting tray having a plurality of rectangular downcomers placed in the bubble area, such that liquid will enter the downcomer opening from two opposite sides. Anti-jump baffles comprising a vertical plate are centrally mounted in the downcomer opening parallel to the longitudinal downcomer sidewalls. According to this publication the anti-jump baffle is present to avoid the sometimes very powerful horizontal movement of suspended liquid droplets above the tray. By placing such a baffle liquid passing horizontally over the downcomer inlet is intercepted and directed into the downcomer.
U.S. Pat. No. 5,547,617 also describes a gas-liquid contacting tray having a plurality of rectangular downcomers placed in the bubble area, such that liquid will enter the downcomer opening from two opposite sides. As in U.S. Pat. No. 5,382,390, an anti-jump baffle is present in the downcomer opening.
When trying to increase the liquid and/or gas flows of the gas-liquid contacting columns as described above a maximum load will be observed. Higher loads will result in that the column fails to function as a liquid-gas contactor or separator due to a phenomena known as flooding. Flooding is described as excessive accumulation of liquid inside the column. The well known flooding mechanisms are downcomer back-up, jet flooding and downcomer choking. These mechanisms are described in Distillation Design, Henry Z. Kister, McGraw-Hill Inc, 1992, pages 267-291. According to this publication downcomer back-up is due to a build-up of liquid inside the downcomer causing the liquid to back-up on the tray leading to liquid accumulation on that tray. The liquid height in the downcomer is determined by the tray pressure drop, liquid height on the tray and frictional losses in the downcomer and downcomer slot area. Jet flooding or entrainment flooding is caused by a too high gas velocity leading to the entrainment of liquid, either by droplets or froth, to the tray above. The liquid will accumulate and leads to flooding. Downcomer choking is caused by a too high aerated liquid velocity in the downcomer. At a certain velocity the friction losses in the downcomer and downcomer entrance become excessive, and the frothy gas-liquid mixture cannot be transported to the tray below, causing liquid accumulation on the tray. With the term froth is to be understood any gas-liquid mixture present on the tray not depending on any flow regime.
German patent publication 764103 describes the use of flat and curved impingement plates in the downcomer opening to limit the froth height in the downcomer, which in turn prevents downcomer back-up. The publication is directed to so-called cross-over trays configurations for use in so-called foaming gas-liquid systems. In such a cross-over configuration the flow of gas-liquid towards the downcomer opening is only from one side. No indication is given that such a plate would prevent downcomer choking.